Measurements of vapor pressures and boiling points, over the range 47 to 780 millimeters of mercury and above ah>out 12° C, were made on 52 purified hydrocarbons. The apparatus consisted of an electricaUy heated boiler, a vapor space with a vertical reentrant tube containing a platinum thermometer having a resistance of 25 ohms, and a condenser. Measurements of the temperature of the liquid-vapor equilibrium were made at 20 fixed pressures maintained automatically. The values of the fixed pressures were determined by calibration of the apparatus with water by using the vapor pressure-temperature tables prepared at the National Bureau of Standards.The experimental data on the hydrocarbons were correlated, the method of least squares being used, with the three-constant Antoine equation for vapor pressures, log P=A-B/(C+t) or t=B/(A-Iog P)-C. Experimental data, together with the values of the three constants of the Antoine equation, applicable over the range of measurement, are reported for 30 paraffin, 4 alkylcyclopentane, 10 alkylcyclohexane, and 8 alkylbenzene hydrocarbons.

A method is described for calculating the properties of hydrocarbons which involves the summation of contributions from component parts of the molecule, together with contributions from interactions between adjacent component parts.For the paraffin hydrocarbons, the calculations were made in terms of the difference in the value of the property between a given normal paraffin and its isomers, and the required constants were evaluated from data on 33 paraffins, CS to Cs. For these paraffins, the average deviation of the calculated from the experimental values is ± 0 .00074 glml in density, ±0.00042 in refractive index (nD at 20° C), and ±0.55° C in the normal boiling point.In the case of the monoolefin hydrocarbons, the calculations were made in terms of the difference in the value of the property between a given mono olefin and the corresponding paraffin having the same carbon skeleton, and the r equired constants were evaluated from data on 58 monoolefins, Cs to Cr. For these monoolefins, the average deviation of the calculated from the experimental values is ±0.0031 glml in density, ± 0.0020 in refractive index (nD at 20° C), and ± 1.33 0 C in the normal boiling point.